This invention relates in general to an apparatus and method for forming tubes and in particular to a new and useful device for extruding a supporting material onto a mandrel along with a profiled material in a manner such that the material arrives at the mandrel in a combined form substantially without any tension.
This invention relates particularly to a device for the production of a tube, container or like cylindrical object (hereafter referred to simply as a tube) from helically wound strip material, more particularly a hollow thermoplastics profile section, in which the strip material is wound onto a mandrel, more particularly a drum, together with a supporting profiled material paid off from a material feeder, more particularly a supporting hose inserted inside the hollow profile section, after leaving the nozzle of an extruder in a deformable state, to produce an obliquely wound assembly welded at the joints between successive turns.
In the production of a tube, having a wall profiled in longitudinal section as determined by a helically wound strip of thermoplastics synthetic material, it is known to wind a profiled material narrower than the strip material helically on a plain mandrel and then to wind thereon the strip material in a deformable state, forming overlapped or abutted, more particularly obliquely abutted, seams between turns of the same helical pitch. In this connection, the strip material is fed warm and in the deformable state from the extruder, and the extruder, which has an appropriately shaped nozzle, is traversed across the rotating mandrel. The profiled material can be wound onto the mandrel simultaneously with the strip material, and the strip material can be deformed over the underlying wrapping or profiled material by rolling or other means.
To save material, the tube is usually formed with a hollow wall, i.e. it is wound from hollow profiled material. In this connection, the preferred supporting profiled material is a hose, preferably a plastics hose, which remains inside the tube wall. The supporting hose is intended to prevent the collapse of the still warm tube profile, in particular because the fully wound tube only cools gradually on the mandrel. However, the problem remains that the supporting profiled material, i.e. the supporting hose, is drawn by the rotating mandrel off the material feeder, which usually consists of a bobbin. The drawing force applied by the mandrel must be sufficiently high to draw the supporting hose off the bobbin and through the extruder nozzle. Because of this relatively high drawing force, however, both the supporting hose and the hollow profiled material, which is still in a deformable state, undergo a certain amount of deformation, so that it is frequently impossible to maintain the desired profile cross-section, with particular reference to the height of the profile, with the result that the profile of the tube becomes non-uniform.